Scientific research and investigation of the influence of continuous exposure to existing environmental alternating electromagnetic fields has led to the adoption of the ALARA (as low as reasonably achievable) rule that calls for use of any protection from magnetic fields that is possible at reasonable costs. It was also recommended that the field level would be limited to 0.2 μT for frequencies in the range of 50 Hz÷300 Hz.
A primary source of magnetic fields in electrical cabinets (e.g., cable/power distribution cabinets) is the bus-bar system from which output branches are distributed from the cabinet through circuit breakers. Thus, people residing in the vicinity of these electrical cabinets are typically exposed to magnetic fields of magnitudes that may exceed minimum requirements set for occupational safety and health. Moreover, devices and communication cables residing in the vicinity of electrical cabinets may suffer from magnetic interferences originating from the magnetic fields emanating from the cabinets.
Heretofore, attempts to reduce the effect of magnetic fields emanating from electrical cabinets mainly suggested partly or fully enclosing the electrical cabinet, or portions thereof, inside magnetic shielding structures made of metallic materials. For example, in order to reach the 0.2 μT field level near electrical cabinets, typically thick metal sheets are used in order to shield the cabinet, or in another possible approach, the electrical cabinet is relocated a certain distance from public areas.
EP 1 763 118 suggests using a metallic protective element serving as a magnetic shield designed to at least partially enclose distribution fuses/connectors of electrical cabinets. This solution focuses on the distribution connectors of the cabinet without considering the magnetic fields emanating from the bar bus system of the cabinet, which is a main source of magnetic fields from cabinets. Furthermore, this solution provides only limited protection due to the need to leave the front part of the metallic protective element open so it may be easily accessed for regular operational purposes and routine maintenance.